Below is every Pokémon confirmed to be obtainable via hatching Eggs - according to avid players on Reddit and the Silph Road - along with their corresponding Egg group.

Note only the first evolution of each chain is available from an Egg - for example Bulbasaur can be hatched from an Egg, but not Ivysaur or Venusaur. That rule is now the same for the new baby Pokémon Togepi, Pichu, Smoochum and co., as they were seemingly counted as pre-evolutions at first and included alongside their evolved forms - for example, Elekid with Electabuzz - in their respective egg groups. To be clear, you can now only get the babies in those evolution chains.